Quarterly report pursuant to Section 13 or 15(d)

Description of Business and Basis of Preparation - Additional Information (Detail)

v3.20.1
Description of Business and Basis of Preparation - Additional Information (Detail) - USD ($)
3 Months Ended
Mar. 31, 2020
Dec. 12, 2019
Sep. 14, 2018
Mar. 31, 2020
Mar. 31, 2019
Dec. 31, 2019
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]            
Accumulated deficit $ (278,430,000)     $ (278,430,000)   $ (271,428,000)
Cash and cash equivalents 20,253,000     20,253,000   41,920,000
Short-term investments 14,267,000     14,267,000   $ 6,494,000
Shelf registration maximum equity offering price $ 127,300,000   $ 175,000,000      
Number of warrants issued to purchase common stock (in shares)     13,198,075      
Aggregate amount receivable upon exercise of warrants     $ 28,600,000      
Warrants, expiration date     Mar. 14, 2019      
Common stock issued, net of expenses       $ 207,000 $ 2,509,000  
Option to Purchase Common Stock            
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]            
Options expiration date   2020-01        
Option to Purchase Common Stock | Maximum            
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]            
Number of options not exercised   5,833,333        
Common Stock            
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]            
Common stock issued, net of expenses (in shares)       285,276 2,226,569  
Common stock issued, net of expenses       $ 1,000 $ 2,000  
Sales Agreement | Common Stock            
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]            
Shelf registration maximum equity offering price     $ 25,000,000      
June 2016 Public Offering            
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]            
Number of warrants issued to purchase common stock (in shares)     4,218,750      
Exercise price of warrants (in dollars per share)     $ 3.00      
March 2018 Public Offering | Series 1 Warrant            
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]            
Number of warrants issued to purchase common stock (in shares)     13,198,075      
Exercise price of warrants (in dollars per share)     $ 1.85      
March 2018 Public Offering | Series 2 Warrant            
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]            
Number of warrants issued to purchase common stock (in shares)     7,988,175      
Exercise price of warrants (in dollars per share)     $ 2.00      
December 2019 Public Offering            
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]            
Number of warrants issued to purchase common stock (in shares)   38,888,889        
Common stock issued, net of expenses (in shares)   38,888,889        
Share price (in dollars per share)   $ 0.90        
Common stock issued, net of expenses   $ 32,500,000        
Underwriters | Maximum            
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]            
Option to purchase shares of common stock   5,833,333        
Underwriters | Warrant liability            
Organization Consolidation And Presentation Of Financial Statements Disclosure [Line Items]            
Number of warrants issued to purchase common stock (in shares)   5,833,333        
Number of warrants exercised   5,833,333